Naphtha boiling range fractions have been used in the manufacture of stocks suitable for use or for blending with other petroleum and petrochemical stocks, to make gasoline motor fuels. A desirable component of a naphtha boiling range fraction for purposes of octane rating has been isopentane. Unfortunately, isopentane has a high vapor pressure (RVP of about 140 kPa) which can result in a gasoline product not meeting governmental standards. See, for instance, U.S. Pat. No. 6,429,349.
While isopentane can be removed from the naphtha boiling range feedstock, the demand for isopentane as a product or an intermediate in petrochemical processes is relatively limited. Moreover, isopentane is a less desirable as a feed to a cracking unit than is normal pentane. Cracking normal paraffins results in a higher product yield than does cracking isoparaffins. A paper entitled “Separation of Normal Paraffins from Isoparaffins” presented by I. A. Reddock, et al, at the Eleventh Australian Conference on Chemical Engineering, Brisbane, Sep. 4-7, 1983 discloses that the ethylene yield of a cracking unit can be increased if it is charged a C5-C9 stream of normal paraffins rather than a typical C5-C9 natural gasoline.
Consequently isopentane is often only of fuel value, e.g., to provide steam for other unit operations. However, often refineries and petrochemical facilities have sufficient waste gas that additional fuel values provided from isopentane removed from naphtha boiling range feedstocks are not needed.
Accordingly, processes are sought that can provide stocks desirable in gasoline applications in a manner that is efficient from capital cost and energy consumption standpoints while converting isopentane into a useful product.